1. Field of the Invention
The present invention relates to a multi-chamber system for carrying substrates such as LCD glass ones (which will be hereinafter referred to as LCD substrates) out of a normal into a decompressed atmosphere to process them in it.
2. Description of the Related Art
The vacuum processing apparatus provided with plural process chambers in which predetermined processes such as etching and ashing are applied to semiconductor wafers and liquid crystal device (LCD) substrates has been used in the course of manufacturing semiconductor devices and LCDs.
In the case of this vacuum processing apparatus, plural or three vacuum process chambers, for example, are arranged around an auxiliary vacuum chamber (or load lock chamber in which a substrate carrier mechanism such as the carrier arm is arranged. LCD substrates, for example, which are to be processed, are carried into and out of the process chambers by the carrier arm and predetermined processes are applied to them in these process chambers.
In the case of the vacuum processing apparatus in which LCD substrates are processed, it is an important technical problem how many sheets of substrates can be processed for a certain time or how the throughput of the apparatus can be enhanced. In addition, LCDs have been used as display devices for large-sized computers and televisions and they therefore become larger and larger in size for this purpose. As they become larger in size, however, the productivity of LCD substrates is reduced and the manufacturing cost per an LCD substrate is increased to greater extent.
One of cases which reduce the productivity as described above resides in that contamination is caused by contaminating matters such as particles in the apparatus. In addition, the shifting of LCD substrates from their predetermined positions is another cause. When they are shifted from their predetermined positions, they are dropped down and damaged while they are being carried, or the uniformity of the process applied to them is degraded. The productivity is thus reduced. Particularly when they become larger in size, they are more likely to be moved by the vacuum-making exhaust of the load lock chamber, for example. They are thus shifted from their predetermined positions.
Further, LCD substrates are various in size and processes applied to these LCD substrates are also various. The vacuum processing apparatus, therefore, must be made more flexible to meet these various sizes and processes.
The detecting of LCD substrates in the load lock chamber is conventionally conducted in such a way that a detecting beam is shot from a photosensor directly to the LCD substrates in the load lock chamber and that beam reflected from the substrates is received by the photosensor. According to this substrate detecting system, however, the reflection factor of the beam is greatly influenced by the surface condition of each substrate. The detecting accuracy of this system is therefore low. The sensibility of the photosensor is adjusted for every LCD substrate in this case, but it takes a large amount of time and effort because each LCD substrate is made of transparent glass.
Further, the photosensor is arranged together with the LCD substrates in a same chamber. The LCD substrates are thus influenced by heat emitted from the photosensor, or bad influence is added to the substrates in the case of sensor trouble. When the sensor is arranged in the load lock chamber, free space in it must be reduced or it must be made larger in size.
The substrate-carrying arm mechanism is arranged adjacent to an opening of the load lock chamber through which the substrates are carried into and out of the load lock chamber. Suction holes are formed in the top of each holder member of the carrier arm mechanism and an O-ring is attached to each of these suction holes. When the substrate is vacuum-sucked on each holder member through the suction holes, it is closely contacted with the O-ring on each holder member along its side rims. Friction and suction forces thus created can prevent each substrate from being positionally shifted on the holder member.
However, the conventional O-rings are made of silicon rubber of fluorine-contained rubber, for example, and when the close contact of the substrate with the O-rings is repeated, particles are caused from the O-rings and they adhere to the substrate.
Further, the LCD substrates (each being about 1.1 mm thick) tend to be made larger, having a size of 550 mm.times.650 mm. When they are held on the holder members, therefore, they bend downward at their center portions because of their own weight. This prevents each substrate from being fully contacted with the O-rings on each holder member along its side rims. The O-rings, sometimes, cannot suck the substrate on the holder member. Particularly when the O-rings are made of hard material, it becomes difficult that the O-rings can vacuum-suck the substrate firmly on the holder member.
During a course of the process, there are also LCD substrates which are being processed, in the processing chamber, and it is not always the case where LCD substrates are held in all the slots of a cassette. Therefore, the presence/absence of a substrate must be confirmed for each slot when LCD substrates are loaded/unloaded by conveying means. The term "slot" is a space or area for storing an LCD substrate.
With the conventional apparatus, optical sensors including laser beam emitters and beam receivers are arranged around a cassette such as to face with each other, and the cassette or the sensors themselves are moved up and down to detect the presence/absence of an LCD substrate for each slot. This operation is a so called mapping operation.
However, the detection of a substrate within a cassette (mapping operation) should be performed for each slot, and therefore it requires a long period of time, decreasing the throughput. Further, for the mapping operation, an ascend/descend drive mechanism for moving a cassette or sensors themselves up and down must be provided. As a result, the number of parts for the apparatus is increased, raising its production cost. In addition, particles are generated from the ascend/descend drive mechanism, and adhered onto an LCD substrate as contamination, reducing the yield. Further, it is very difficult to adjust the optical axis of the beam emitter of an optical sensor to be aligned with that of a beam receiver.